Stratum Response Analysis Of Large Diameter Shield Tunnel Construction In Urban Dense Area

In recent years,with the rapid growth of national economy and extensive investment in infrastructure,urban underground space construction has witnessed great development.Shield tunnel construction,as an effective tool for urban underground space construction,plays an increasingly important role in urban subway,municipal corridor and high-speed railway tunnel construction.In order to effectively control the safety of the tunnel itself and the surrounding buildings,it is necessary to deeply understand the deformation characteristics,deformation mechanism and control measures of stratum response under different shield construction conditions.Tunnel construction in urban core area has stricter control requirements for stratum deformation due to the variety of important buildings,the complexity of Metro highway traffic and the intricate distribution of various underground pipelines around it.Therefore,it is of great significance to study and analyze the stratum response of large-diameter shield tunnel construction in urban intensive area.Based on the research background of Tsinghua tunnel 3#-2#shield tunneling section,this paper statistically analyzed the deformation development rules of surface subsidence and horizontal displacement at different construction stages under different strata conditions,and considered the influence of shield tunneling construction parameters.Numerical simulation software was used to analyze the deformation rules of surface subsidence and horizontal displacement under different strata conditions in the shield tunneling area.Meanwhile,the influence database of 90 groups of model parameters was established to analyze the influence of tunnel geometric parameters,engineering geological parameters and shield construction parameters on the maximum settlement value.BP and optimized BP,custom neural network and time series prediction model were established to realize real-time prediction of surface subsidence and horizontal displacement during construction.Based on genetic algorithm,the control analysis of construction parameters of shield tunneling is completed,and the main control measures of formation deformation during construction are proposed.The main research results include:(1)Based on the measured data and the recorded parameters of shield tunneling,the characteristics of ground surface subsidence and horizontal displacement deformation under different strata conditions,the variation law of shield tunneling parameters in different stages and the correlation between parameters are analyzed and completed.The long-term deformation of surface subsidence presents a "s-shaped" distribution,which can be well fitted by Logistic function.The horizontal surface subsidence in five stages presents a "u-shaped" groove distribution,and the Peck empirical formula can be well fitted.The horizontal displacement of stratum presents the distribution of "inclined L type" and "convex type"respectively under different stratum conditions,and the development rule of horizontal displacement along the direction of depth is found by incremental analysis.The shield construction parameters will change in different stages under different stratum conditions,and show different degrees of correlation with each other,but they are strongly related to stratum deformation,and the recommended values of shield construction parameters in different shield sections can be given through theoretical calculation.(2)By using numerical simulation software,the range of stress release coefficient of tunnel excavation in engineering construction and the development law of ground surface settlement and horizontal displacement under different soil layers in excavation area are analyzed respectively,and 90 sets of multi-parameter analysis database of model are established to analyze the influencing factors of stratum response.The formation stress release coefficient suitable for this project is determined to be within the range of 0.12?0.14 through two-dimensional numerical model simulation and field measured data.It is found that the surface subsidence and horizontal displacement have different deformation rules under three soil layers of sandy pebble soil,silty clay or sandy pebble soil mixed with silty clay.The influence model database of 90 groups of three-dimensional maximum surface subsidence parameters was established to analyze the influence of geometric parameters,engineering geological parameters and shield construction parameters of each tunnel on the formation deformation one by one,and the simulation results were fitted and analyzed.(3)Neural network,principal component analysis,genetic algorithm and time series were applied to establish the multi-parameter prediction model of maximum surface settlement and the diachronic development prediction model of surface settlement and horizontal displacement.Four multi-parameter prediction models of maximum surface subsidence,including traditional BP,PCA-BP,GA-BP and PAC-GA-BP,are established by using traditional BP neural network and combining principal component analysis(PCA)and genetic algorithm(GA)to achieve the prediction of maximum surface subsidence and to compare the prediction results of each model synthetically.The traditional ARMA time series model and the nonlinear autoregressive neural network(NARNN and NARXNN)model were used to realize the real-time prediction of surface subsidence and horizontal displacement of measurement points,and the three prediction models were comprehensively evaluated.(4)Based on the extremum optimization function of genetic algorithm,the extremum optimization model of shield construction parameters in standard sections of shield tunneling under different strata conditions is established.Through this model,the control values of shield construction parameters are obtained,and the main control measures of stratum deformation during shield tunneling are proposed.By comparing the control values of shield construction parameters in each standard section with the actual statistical mean values of parameters and theoretical calculation values,the rationality of the obtained control values is illustrated,and the final recommended safety interval of shield construction parameters is obtained by setting relevant engineering safety factors,which has important guiding significance for practical engineering.At the same time,the main influencing factors of stratum deformation during shield tunneling are summarized.In order to realize effective control of stratum response during construction,it is proposed that effective control measures can be adopted in three aspects:shield tunneling parameters control,active auxiliary construction method control and information management control.